Apparatus comprising a single photon photodetector having reduced afterpulsing and method therefor

ABSTRACT

A single-photon detector is disclosed that provides reduced afterpulsing without some of the disadvantages for doing so in the prior art. An embodiment of the present invention provides a stimulus pulse to the active area of an avalanche photodetector to stimulate charges that are trapped in energy trap states to detrap. In some embodiments of the present invention, the stimulus pulse is a thermal pulse.

STATEMENT OF RELATED CASES

This case is a division of co-pending U.S. patent application Ser. No.11/277,562 filed Mar. 27, 2006, which is incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to avalanche photodetectors in general,and, more particularly, to single-photon avalanche photodetectors.

BACKGROUND OF THE INVENTION

A semiconductor photodetector generates a free-carrier pair(electron-hole) when it absorbs a photon. When the photodetector issubjected to an electric field (by the application of a bias voltage tothe photodetector), free-carriers generated in the photodetector giverise to a macroscopic electric current.

A useful photodetector is characterized by high overall efficiency andhigh sensitivity. Efficiency can be defined as the number of freecarriers that are generated per incident photon. Consequently, highefficiency implies a high generated current for a given incident opticalpower. Sensitivity is characterized by the minimum optical signal thatgives rise to a current that can be distinguished from the backgroundcurrent due to noise (e.g., dark current, thermal noise, Johnson noise,1/F noise, etc.).

One widely-used type of photodetector is the avalanche photodetector.Avalanche photodetectors have high sensitivity and, in fact, can be madesensitive enough to detect even a single photon. Avalanchephotodetectors are so named because of the “avalanche” of free-carrierpairs that is generated by the detector. The “avalanche” is the resultof a multiplication of the free-carrier pairs, The multiplication occurswhen the free-carrier pairs that were generated by incident photons areaccelerated to high energies by an applied reverse bias voltage. As theaccelerated free carriers travel through the multiplication region ofthe avalanche photodetector, they collide with bound carriers in theatomic lattice of the multiplication region, generating more freecarriers through a process called “impact ionization.”

The current flow in the avalanche photodetector is directly related tothe number of free carriers generated from electron-hole pairs. The gainof a photodetector (i.e., the increase in the number of free carrierpairs) is a function of the reverse bias voltage applied to thephotodetector.

An avalanche photodetector is characterized by a “breakdown voltage.”When the avalanche photodetector is biased above its breakdown voltage,carrier generation can become self-sustaining and result in run-awayavalanche. In order to function as a single-photon detector, anavalanche photodetector is biased above its breakdown voltage. This isreferred to as “arming” the avalanche photodetector. Once the detectoris armed, the single free carrier created by the absorption of a singlephoton can create a runaway avalanche resulting in an easily detectablemacroscopic current. It is also possible for a free carrier to becreated by mechanisms other than photon absorption (e.g., thermalexcitation and carrier tunneling). These “dark” carriers can give riseto the same easily detectable macroscopic current, in this case referredto as false counts, or “dark counts.” Dark counts constitute noise in asingle-photon avalanche detector, and therefore reduce its sensitivity.

After a photon (or dark count) is detected, it is necessary to stop theself-sustained avalanche in order to make further use of the detector.In order to halt the avalanche process, the bias voltage of theavalanche photodetector is reduced below its breakdown voltage. Thisprocess is referred to as “quenching” the avalanche photodetector.Although quenching stops the avalanche process, not all free carriersare swept out of the avalanche region. Instead, some carriers becometrapped in trap states that exist in the multiplication region due tocrystalline defects or other causes which create energy levels withinthe semiconductor band gap of the multiplication region material.

At a later time, trapped carriers “detrap,” again becoming freecarriers. These detrapped carriers can become an additional source ofdark counts. The creation of additional dark counts caused by spurious,uncontrolled emission of trapped charges after quenching is referred toas “afterpulsing.” Afterpulsing raises the total dark count rate abovethe baseline dark count rate established by thermal carrier emission andcarrier tunneling in the absence of afterpulsing. Since any increase ofdark count rate degrades the performance of a single-photon detector,elimination of afterpulsing is of great interest.

Several strategies exist in the prior art for reducing afterpulsing.Trapped charges will generally become free carriers in random fashiondue to their thermal emission from the trap. Therefore, one approachused is to simply wait a sufficient period of time after quenching toallow trapped charges to detrap on their own (i.e., the inherent“detrapping time.” If the inherent detrapping time is long, thisapproach leads to an undesirably long period of time when thesingle-photon detector is inoperable. In gated-mode operation, wherein abias voltage pulse is periodically applied to arm the avalanchephotodetector (i.e., a “gating pulse”), simply waiting for thermalemission of trapped carriers reduces the repetition rate at which singlephotons can be measured.

A second prior-art approach for reducing afterpulsing is to operate thesingle-photon detector at an elevated temperature to promote detrapping.But operating at an elevated temperature results in an increase in thebaseline dark count rate due to an increase in thermal carrier emissionand carrier tunneling processes.

In a third prior-art approach for reducing afterpulsing, trappedcarriers are photoionized via “sub-band illumination.” In this approach,the photodetector is illuminated by a beam of light. The energy of thephotons in this beam of light is a function of the wavelength of thelight. Photons in longer-wavelength light have relatively lower energythan photons in shorter-wavelength light. The wavelength of light usedin this prior-art approach is selected to provide photoionization energysufficient only to detrap carriers, but insufficient to liberatecarriers that are not in trapped states.

To avoid the detection of the sub-band illumination by thephotodetector, the wavelength of light used for sub-band illuminationmust be longer than the detection limit, or “cutoff wavelength,” of theabsorbing material in the photodetector. In the case of anindium-phosphide-based avalanche photodetector with anindium-gallium-arsenide absorbing material, the wavelength of light usedfor sub-band illumination is greater than 1700 nanometers.

There exists a need, therefore, for a single-photon detector withreduced afterpulsing that overcomes some of the limitations of the priorart.

SUMMARY OF THE INVENTION

The present invention enables single photon detection without some ofthe costs and disadvantages for doing so in the prior art. For example,embodiments of the present invention enable high-repetition-rategated-mode operation of a single-photon detector.

In accordance with the illustrative embodiment of the present invention,trapped carriers in the photodetector are excited by a pulse ofstimulating energy, such as a thermal pulse. This proactive excitationof trapped carriers clears energy trap states. This reduces theprobability of random emissions of these carriers, as might otherwiseoccur in the absence of the stimulus (e.g., during conventionaloperation as a single-photon detector, etc.). As a result, the darkcount rate of the photodetector during single-photon operation isreduced.

Embodiments of the present invention, like the prior art, use anavalanche photodetector that is biased above its breakdown voltage todetect the incidence of a single photon. Like the prior art, someembodiments of the present invention proactively excite carriers thatare in energy trap states, thereby reducing afterpulsing. But unlike theprior art, in the illustrative embodiment of the present invention,trapped carriers are only temporarily excited.

More particularly, in the prior art, photodetectors have been operatedat an elevated temperature to stimulate the emission of trapped carriersfrom energy trap states. These photodetectors remain at this elevatedtemperature during operation as a single-photon detector. As a result,prior-art single-photon photodetectors are subject to high dark countrates. In contrast, the present invention applies only a Pulse ofthermal energy to the photodetector to temporarily raise the temperatureof a photodetector. The photodetector is not operated in single-photondetection mode during the application of the stimulating pulse. Thethermal pulse substantially clears energy trap states of carriers sothat the photodetector has a reduced dark count rate when it issubsequently operated as a single-photon photodetector.

An embodiment of the present invention comprises: an avalanchephotodetector having a multiplication layer comprising a multiplicationregion; and a stimulator, wherein the stimulator provides a stimuluspulse, and wherein the stimulus pulse detraps electrical carriers in theavalanche photodetector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic diagram of the salient components ofsingle-photon detection system 100 according to an illustrativeembodiment of the present invention.

FIG. 2 depicts a schematic diagram of the salient components of aphotodetector according to an illustrative embodiment of the presentinvention.

FIG. 3 depicts a representative timing diagram for photodetector gatingand thermal pulsing, according to the illustrative embodiment of thepresent invention.

FIG. 4 depicts a method of operating a photodetector as a single-photondetector in gated-mode operation.

DETAILED DESCRIPTION

The following terms are defined for use in this Specification, includingthe appended claims:

-   -   Monolithically-integrated means formed either: (1) in the body        of a layer or substrate, typically by etching into the layer or        substrate or; (2) on the surface of the layer or substrate,        typically by patterning layers disposed on the surface.    -   Thermal-cycling means temporarily changing a temperature to        cause an effect. An example of thermal-cycling is the        rapid-thermal annealing of a substrate to induce crystal growth        or stress relaxation.    -   Pulse means a brief sudden change in a normally constant        quantity. Examples of pulses include, without limitation: (1) a        thermal pulse, wherein a short rapid increase in the temperature        of an element or portion of an element is produced; and (2) a        voltage pulse, wherein a short rapid increase in a voltage is        produced.    -   Multiplication region means a region of an avalanche        photodetector wherein avalanche gain predominantly occurs.

FIG. 1 depicts a schematic diagram of the salient components ofsingle-photon detection system 100 according to an illustrativeembodiment of the present invention. Single-photon detection system 100comprises photodetector 102, stimulator 104, stimulus sink 106, andcontroller 108. Single-photon detection system 100 is a system thatprovides a macroscopic current in response to the incidence of a singlephoton on photodetector 102.

Photodetector 102 is an indium-phosphide-based avalanche photodetectorhaving separate absorption and multiplication regions. Photodetector 102will be described in detail below and with respect to FIG. 2. In someembodiments, photodetector 102 is an avalanche photodetector formedusing material systems other than indium-phosphide. It will be clear tothose skilled in the art, after reading this specification, how to makeand use embodiments of the present invention that comprise avalanchephotodetectors that are based on any suitable material system.

Stimulator 104 is a stimulator for providing a pulse of stimulatingenergy to electrical carriers that have become trapped in energy leveltraps in the multiplication region of photodetector 102. The energyprovided by stimulator 104 proactively excites the trapped carriers outof their energy trap states. In other words, the pulse of stimulatingenergy “detraps” the trapped carriers. During the time when stimulatingenergy is being applied to photodetector 102, the photodetector isbiased below breakdown and can not detect either incident photons ordark carriers. Therefore, photodetector 102 is inoperative forsingle-photon detection during the duration of the stimulus pulse. Afterthe pulse of stimulating energy ends, however, photodetector 102 canagain be made operative for single-photon detection. In someembodiments, stimulator 104 provides stimulating energy to photodetector102 as a whole. In some other embodiments, stimulator 104 providesstimulating energy to a selected portion or portions of photodetector102.

Stimulus sink 106 is an element for drawing stimulating energy away fromthe active area of photodetector 102. Stimulus sink 106 facilitates arapid decay of the stimulating energy in the active area ofphotodetector 102, which thereby shortens the time during whichphotodetector 102 is inoperative for single-photon detection. In someembodiments, stimulus sink 106 is a passive element, such as a highstimulus-conductivity path that facilitates the conduction of thestimulus away from the active area of photodetector 102. In some otherembodiments, stimulus sink 106 is an active element that draws thestimulus away from the active area of the photodetector 102.

Controller 108 is a general purpose processor and power supply.Controller 108 provides a bias voltage to photodetector 102, receiveselectrical signals from photodetector 102, stores and processes data,and provides power and control signals to stimulator 104 and stimulussink 106. In the illustrative embodiment of the present invention,controller 108 controls the sequence of arming photodetector 102,quenching photodetector 102, and stimulating trapped carriers inphotodetector with a stimulus pulse, and actively sinking stimulatingenergy from photodetector 102. In some embodiments of the presentinvention, stimulus sink 106 is a passive element that does not requirecontrol by controller 108.

FIG. 2 depicts a schematic diagram of the salient components of aphotodetector according to an illustrative embodiment of the presentinvention. Photodetector 102 comprises substrate 202, absorption layer204, grading layer 206, field control layer 208, layer 210, andpassivation layer 212. Layer 210 comprises active region 218, whichcomprises diffused-region 214 and multiplication region 216.

FIG. 2 depicts avalanche photodetector 102 integrated with heater 220and Peltier cooler 222.

Substrate 202 is a substrate suitable for use in the formation of anavalanche photodetector, as is well-known in the art.

Absorption layer 204 is a lightly-doped layer of indium gallium arsenide(InGaAs) with low band-gap energy. It will be clear to those skilled inthe art how to make and use absorption layer 104.

Grading layer 206 is an n-doped indium gallium arsenide phosphide(InGaAsP) layer that smoothes the interface between absorption layer 204and field control layer 208.

Field control layer 208 is a moderately n-doped layer of indiumphosphide. Field control layer 208 enables maintenance of a low electricfield in absorption layer 204, while supporting a high electric field inmultiplication region 216. It will be clear to those skilled in the arthow to make and use field control layer 208.

Multiplication layer 210 is an intrinsic layer of indium phosphide.Within multiplication layer 210 is active region 218 which includesdiffused-region 214 and multiplication region 216. Active region 218 isformed by diffusing a high level of p-type dopant into multiplicationlayer 210 to form diffused region 214. The extent of diffused region 214forms a p-n junction. The undoped portion of active region 218 formsmultiplication region 216. Avalanche multiplication occurs substantiallyin multiplication region 216. In some embodiments of the presentinvention, multiplication layer 210 is a lightly n-doped layer of indiumphosphide and diffused region 214 is heavily doped with a p-type dopant.In some other embodiments, multiplication layer 210 is a lightly p-dopedlayer of indium phosphide and diffused-region 214 is heavily doped withan n-type dopant. It will be clear to those skilled in the art, afterreading this specification, how to make and use embodiments of thepresent invention in which multiplication layer 210 is other than anintrinsic layer of indium phosphide.

Passivation layer 212 is a layer of silicon nitride that has a thicknessof 100 nanometers. In some other embodiments, passivation layer 212 hasa thickness other than 100 nanometers. In some embodiments, passivationlayer 212 comprises thinned regions on which heater 220 and/or Peltiercooler 222 are disposed to facilitate thermal conduction to and fromheater 220 and/or Peltier cooler 222. It will be clear to those skilledin the art, after reading this specification, how to make and usepassivation layer 212.

Heater 220 is a thin-film resistive heater having a semi-annular shape,which is deposited on top of passivation layer 212 just outside thelateral extent of active region 218. Stimulator 104 comprises heater220, as described above and with respect to FIG. 1. When an electriccurrent is provided to heater 220 by controller 108, heater 220 rapidlyheats active region 218. In the illustrative embodiment, the duration ofelectric current pulses is less than 50 nanoseconds. In someembodiments, the duration of electric current pulses can be as long asseveral hundred nanoseconds. In some embodiments, electric currentpulses as short as 1 to 5 nanoseconds are used. The duration of thecurrent pulse (and, therefore, the heat pulse in active region 218)influences the repetition rate at which detrapping can occur. It will beclear to those skilled in the art, after reading this specification, howto make and use alternative embodiments of the present invention thatutilize electric current pulses to heater 220 that are other than 50nanoseconds in duration.

In the illustrative embodiment, heater 220 and photodetector 102 aremonolithically-integrated. In some alternative embodiments of thepresent invention, heater 220 and photodetector 102 are notmonolithically-integrated. In yet some further embodiments of thepresent invention, heater 220 radiates heat to at least a portion ofphotodetector 102. It will be clear to those skilled in the art, afterreading this specification, how to make and use embodiments of thepresent invention wherein heater 220 and photodetector 102 are notmonolithically-integrated.

In the illustrative embodiment, thermal energy is the stimulating energyfor detrapping trapped carriers in photodetector 102. In somealternative embodiments, thermal energy is imparted to active region bypulsing optical energy onto photodetector 102. The wavelength of thisoptical energy is chosen such that active region 218 will absorb asignificant amount of the optical energy and convert it to thermalenergy. Suitable wavelengths for this optical energy include those equalto or less than 900 nanometers when the active region comprisesindium-phosphide. For embodiments that include a different active regionmaterial, suitable wavelengths will be those for which the photon energyis greater than the band gap energy of the active region material.

In some alternative embodiments, thermal energy is imparted to activeregion 218 by pulsing optical energy onto an absorption layer depositedon photodetector 102. Suitable materials for use in absorption layersinclude, without limitation, silicon, silicon dioxide, silicon nitride,silicon carbide, tungsten, titanium, titanium-tungsten, titaniumnitride, and organic materials. In some embodiments, the wavelength ofthe optical energy can be greater than 900 nanometers, since suitablewavelengths for the optical energy will be dependent upon the absorptioncharacteristics of the materials used in the absorption layer.

In the illustrative embodiment, stimulator 104 comprises heater 220,which stimulates trapped charges with pulses of thermal energy. In someother embodiments, stimulator 104 stimulates trapped charges with pulsesof other forms of energy. It will be clear to those skilled in the art,after reading this specification, how to make and use alternativeembodiments of the present invention that comprise stimulators thatstimulate trapped charges with pulses of such other forms of energy.

Peltier cooler 222 is a thermo-electric cooler having an annular shape,as is well-known in the art. Peltier cooler 222 facilitates the rapidremoval of heat from active region 218 after heater 220 has turned off.Peltier cooler 222 composes stimulus sink 106 as described above andwith respect to FIG. 1. The speed at which Peltier cooler 222 removesheat from active region 218 influences the repetition rate at whichdetrapping can occur and the percentage of time in which single-photondetection system 100 is operative.

In some alternative embodiments of the present invention, a passivestimulus sink is used rather than an active stimulus sink. For example,in some of these embodiments, a thick-film metallization is used, ratherthan Peltier cooler 222, to provide a low thermal resistance path toconduct heat away from active region 218.

In still some other embodiments of the present invention, heater 220 andPeltier cooler 222 are combined into a single element. For example, aPeltier device can be used to either heat or cool, depending on the flowof current through it. Therefore, in these embodiments, Peltier device222 provides both heating and cooling functions.

FIG. 3 depicts a representative timing diagram for photodetector gatingand thermal pulsing, according to the illustrative embodiment of thepresent invention. Timing diagram 300 depicts the relationship betweengate pulse train 302 and thermal pulse train 304. Gate pulse train 302is a graphic representation of the bias voltage applied to photodetector102.

In order to more clearly demonstrate the present invention, operation ofphotodetector 102 as a single-photon detector is described here, withreference to FIGS. 2, 3 and 4.

FIG. 4 depicts a method of operating a photodetector as a single-photondetector in gated-mode operation. Since gated-mode operation comprises arepetitive cycle, only one such cycle is described here. In thegated-mode operation of photodetector 102, photodetector 102 is biasedat a baseline voltage below its breakdown voltage, V_(br). In order toarm photodetector 102, a gate pulse that increases the bias voltageabove V_(br) is applied to photodetector 102. The gate pulse has agate-pulse period T_(p) and a gate-pulse width of T_(g). At the end ofthe gate pulse (i.e., at T_(g)), photodetector 102 is quenched byreducing the bias voltage once again below V_(br). Therefore, whenphotodetector 102 detects a photon during a gate pulse, the resultingavalanche current signal is limited to the remainder of that gate pulse.At the end of that gate pulse, photodetector 102 is quenched by reducingthe bias voltage back below V_(br) to stifle the avalanche current.

Method 400 begins with operation 401, wherein photodetector 102 is armedfor single-photon detection. To arm photodetector 102, processor 108provides a bias voltage to photodetector 102 that is above its breakdownvoltage, V_(br). Operation 401 is depicted in FIG. 3 as the rising edgethe first pulse of gate pulse train 302.

At operation 402, photodetector 102 is quenched by reducing the biasvoltage below V_(br). To quench photodetector 102, processor 108provides a bias voltage to photodetector 102 that is below its breakdownvoltage, V_(br). This is depicted in FIG. 3 as the falling edge of thefirst pulse of gate pulse train 302. The time between operations 401 and402 is equal to gate pulse width T_(g), which in some embodiments of thepresent invention is approximately equal to 1 nanosecond.

At operation 403, active area 218 of photodetector 102 is provided witha stimulus to excite trapped carriers from their trapped states (i.e.,cause them to detrap). In the illustrative embodiment, the stimuluscomprises application of heat to active area 218. To heat active area218, controller 108 provides electric current to heater 220. Operation403 is depicted in FIG. 3 as the rising edge of the first pulse inthermal pulse train 304.

At operation 404, the stimulus applied to photodetector 102 is removed.To remove the stimulus, controller 108 stops the flow of electriccurrent to heater 220 and provides electric current to Peltier cooler222 to cause it to begin cooling active area 218. Operation 404 isdepicted in FIG. 3 as the falling edge of the first pulse in thermalpulse train 304. The time between operations 403 and 404 is equal tothermal pulse width T_(t), which in some embodiments of the presentinvention is in the range of sub-nanosecond to tens of nanoseconds, andin some embodiments is approximately equal to 1 nanosecond. In someembodiments of the present invention, which employ a passive stimulussink, operation 404 does not include the provision of electric currentto Peltier cooler 222.

After operation 404, photodetector 102 is ready to be armed forsingle-photon detection again. Since each gate pulse is followed by athermal pulse to excite trapped carriers in photodetector 102 from theirtrapped states, the periodicity of method 400 is also equal to T_(p). Insome embodiments of the present invention, the sequence of temporallyinterleaved gate pulses and thermal pulses can be non-periodic.

Immediately after quenching photodetector 102, a thermal pulse isapplied to photodetector 102 to heat active region 218. When activeregion 218 is heated, trapped carriers are stimulated to detrap. Therate at which trapped carriers detrap is a function of the temperatureof active region 218 (i.e., they detrap more quickly at highertemperatures). The duration of the thermal pulse, T_(t), is a functionof the detrap rate, but can be as short as one nanosecond. Once thethermal pulse has ended (i.e., after T_(t)), photodetector 102 can bearmed again. It should be noted that it is not necessary to wait untilthe temperature of active region 218 has dropped all the way to its basetemperature before arming photodetector 102. Significant improvement inafterpulsing performance can be obtained from inducing a sufficienttemperature swing between detrapping and application of a gate pulse.

In the prior art, T_(p) is typically limited to at least tens ofmicroseconds due to the time required to passively detrap trappedcarriers. In contrast, the present invention utilizes active detrappingof trapped carriers by stimulating them to detrap. The presentinvention, therefore, enables gated-mode operation having a gate-pulseperiod, T_(p), as short as 1 to 5 nanoseconds.

Therefore, photodetector 102 is armed during gate-pulse width, T_(g).Timing diagram 300 depicts gated-mode operation with periodicity, T_(p),equal to 50 nanoseconds.

Although the illustrative embodiment describes operation ofphotodetector 102 in gated-mode operation, it will be clear to thoseskilled in the art, after reading this specification, how to make anduse alternative embodiments of the present invention that compriseoperation of photodetector 102 in non-gated-mode operation. For example,in some alternative embodiments of the present invention, photodetector102 remains armed until a photon is detected. Once photon detection hasoccurred, photodetector 102 is quickly quenched and a thermal pulse isapplied to photodetector 102 to detrap trapped carriers. Subsequent tothe thermal pulse, photodetector 102 is armed again to await detectionof another photon.

In some embodiments of the present invention, photodetector 102 remainsarmed until controller 108 quenches and detraps it. In some embodimentsof the present invention, controller 108 will quench, detrap, and armphotodetector 102 in response to the receipt of a stimulus by controller108. In some embodiments of the present invention, controller 108 willquench, detrap, and arm photodetector 102 at the request of an operator.In some embodiments of the present invention, controller 108 willquench, detrap, and arm photodetector 102 after satisfaction of a presetcondition, such as a duration between photon detections that exceeds amaximum time-period.

It is to be understood that the above-described embodiments are merelyillustrative of the present invention and that many variations of theabove-described embodiments can be devised by those skilled in the artwithout departing from the scope of the invention. For example, in thisSpecification, numerous specific details are provided in order toprovide a thorough description and understanding of the illustrativeembodiments of the present invention. Those skilled in the art willrecognize, however, that the invention can be practiced without one ormore of those details, or with other methods, materials, components,etc.

Furthermore, in some instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of the illustrative embodiments. It is understood that thevarious embodiments shown in the Figures are illustrative, and are notnecessarily drawn to scale. Reference throughout the specification to“one embodiment” or “an embodiment” or “some embodiments” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment(s) is included in at least one embodimentof the present invention, but not necessarily all embodiments.Consequently, the appearances of the phrase “in one embodiment,” “in anembodiment,” or “in some embodiments” in various places throughout theSpecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, materials, orcharacteristics can be combined in any suitable manner in one or moreembodiments. It is therefore intended that such variations be includedwithin the scope of the following claims and their equivalents.

1. An article comprising: an avalanche photodetector having a firstlayer comprising a multiplication region including traps; a stimulatorcomprising a thin-film resistive heater; and a second layer that iselectrically insulating, wherein the avalanche photodetector, theheater, and the second layer are monolithically integrated with eachother, wherein the second layer interposes the first layer and theheater, conducts heat between the heater and the first layer, andelectrically insulates the first layer from the heater, wherein thestimulator is operatively arranged to provide a pulse of thermal energyto the multiplication region, and wherein the thermal energy detrapselectrical carriers in the traps of the multiplication region.
 2. Thearticle of claim 1 further comprising a controller, wherein thecontroller controls the stimulator.
 3. The article of claim 1 whereinthe avalanche photodetector further comprises a stimulus sink thatfacilitates removal of the thermal energy from the multiplicationregion.
 4. The article of claim 3 further comprising a controller,wherein the controller controls the stimulus sink and the stimulator. 5.The article of claim 1 wherein the pulse has a duration less thanapproximately 50 nanoseconds.
 6. The article of claim 5 wherein theduration is within the range of approximately 1 nanosecond toapproximately 5 nanoseconds.
 7. An article comprising: an avalanchephotodetector, wherein the avalanche photodetector is dimensioned andarranged to provide an electrical signal in response to the receipt of asingle photon, wherein the avalanche photodetector comprises: a firstlayer comprising a multiplication region including traps; a stimulatorcomprising a thin-film heater; and a second layer that is electricallyinsulating, wherein the avalanche photodetector, the heater, and thesecond layer are monolithically integrated with each other, wherein thesecond layer interposes the first layer and the heater, conducts heatbetween the heater and the first layer, and electrically insulates thefirst layer from the heater, wherein the heater is operatively arrangedto provide a pulse of thermal energy to the multiplication region, andwherein the thermal energy detraps electrical carriers in the traps ofthe multiplication region.
 8. The article of claim 7 wherein the pulsehas a duration that is less than or equal to approximately 50nanoseconds.
 9. The article of claim 8 wherein the duration is withinthe range of approximately 1 nanosecond to approximately 5 nanoseconds.